Post on 13-Feb-2018
Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 2 ….2016
211
EXPERIMENTAL PERFORMANCE OF REINFORCED CONCRETE
HOLLOW COLUMNS EXPOSED TO FIRE
Dr.Thaar Saud Salman Al-Gasham
Civil Engineering Department, College of Engineering, University of Wasit.
E-mail: dr.thaaralgasham@yahoo.com, Mobile: 07813053254.
Received 10 January 2016 Accepted 21 February 2016
ABSTRACT
This paper experimentally investigates the effect of high-temperature fire on the structural behavior of
reinforced concrete hollow columns. Sixteen square (120×120mm) columns were fabricated with
600mm length. The experiment's parameters were: the hollow size and the temperature of fire. Twelve
specimens were cast with a hollow cross-section by inserting PVC pipes centrally along their length;
these columns were categorized into three groups depending on the hollow diameters: 25.4, 50.8, and
76. 2mm. The remaining samples were solid and gathered in one group. Each group contained four
samples; three of them were burnt at 300, 500, and 700 oC for one hour, and the fourth one was a
reference not exposed to fire. All columns were tested under an axial compressive loading applied
progressively up to the column’s collapse. The experiment results indicated that the collapse load of
columns, having a same cross-sectional area, decreased with increased the temperature. The decline in
columns’ strength ranged from 20.00% to 68.67% for specimens exposed to 300-700oC temperature,
respectively. Additionally, for columns exposed to the same temperature, the collapse load descended
as the hollow size augmented. A decrease of failure load varied from 21.86% to 65.38% for 25.4
to76.2mm hollow size columns, respectively. Finally, columns' stiffness reduced with increasing the
temperature and the hollow size.
Keywords: hollow columns, fire exposure, temperature, collapse load, axial stiffness.
معدة الررانية الدلحة ألدجفة ألدررة أل ألان ألأالداء ألتجريبي ل
د.ثنئر ارفد احدنن الغشنمم.
كحة الهاةا / جنمر وااط
ألرالص
تجريبيا تأثير الحرارة المرتفعة على السلوك االنشائي لالعمدة الخرسانية المسلحة المجوفة. تم أنشاء ستة عشرة عمود البحث يتحرى
ملم . متغيرات التجربة كانت كال من حجم التجويف و درجة الحرارة . اثنى عشر 011ملم وبطول مقداره 021× 021بعاد مربع با
مركزيا على طول العينة. تم تصنيف هذه العينات باالعتماد على قطر (PVC) عينة كانت مجوفة من خالل مد أنبوب بالستيكي
Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 2 ….2016
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ج المتبقية كانت ذات مقطع صلد و جمعت في مجموعة واحدة. كل مجموعة تحتوي على النماذملم(. 20.2و 1.5.و 2..2االنبوب )
م ( والنموذج الرابع هو نموذج مصدري لم يتعرض 211و 11.و 011اربع نماذج, ثالث منها معرضة الى درجات حرارة مختلفة )
الى حد الفشل. نتائج التجربة يجيا على النموذج سلط تدرمالى النار. جميع االعمدة تم فحصها من خالل تسليط حمل انضغاط محوري
شل بحمل يتناقص مع ازدياد درجة الحرارة. ان النقصان في مقاومة االعمدة فبينت ان االعمدة ذات المقطع العرضي المتشابه ت
االعمدة باالضافة الى ذلك ان م. 211الى 011% عند تعرضها الى درجة حرارة تتراوح من 05.02% الى 21من تترواح
% 20.50المعرضة الى نفس درجة الحرارة فشلت بحمل يتناقص مع ازدياد حجم التجويف. حيث تغير االنخفاض في حمل الفشل من
ملم. أخيرا, ان صالبة االعمدة تنخفض مع ازدياد كال من درجة 20.2ملم الى 2..2تجويف يتراوح من % لالعمدة ذات 05..0الى
. وحجم التجويف الحرارة
1. INTRODUCTION
The hollow reinforced concrete columns are desirable to employ in constructions, especially in seismic
zones because of minimizing the superstructures’ weight and subsequently the seismic response. The
using of hollow columns reduces the loadings transferred to foundations; hence smaller foundations
are required. Therefore, hollow columns are an economic choice in areas where the concrete cost is
comparatively high. Finally, the hollow columns allow easy to access different services like pipes for
electric wiring and plumbing (Kim et al., 2012).
The exposure to high temperature is one of the risk issues facing the constructions. The structural
elements should be designed with an adequate resistance to fire in order to protect the structures from a
collapse, or at least, provide suitable time for occupants to escape before the collapse. The columns are
the most important elements in constructions since they shore the structures and carry the loads to the
footings. Therefore, any column deterioration may lead to a partial or complete collapse of the
structure (Sakai and Sheikh, 1989).
The local and international areas have seen many studies investigating the effect of fire exposure on
the structural elements, especially for columns. In 2005, Kodur et al., examined the behavior of three
confined reinforced concrete columns using Fiber -Reinforced Polymer (FRP) sheets and exposed to
fire. The cross-sections of two specimens were circular (400 mm in diameter), and the third specimen
was square (406 mm in width). The length of three columns was 3810mm. The experimental results
observed that the FRP sheets were sensible to the influences of high temperatures and needed a
suitable fire protection. The well protected strengthened columns performed structurally better than the
unstrengthened columns.
The behavior of axially loaded reinforced self-compacting concrete was investigated experimentally by
Izzat in 2012. Twelve columns were exposed to various temperatures (300, 500, and 700 oC); two
methods for cooling were used; gradually by air and suddenly using water spray. The results revealed
that the failure loads of the column decreased with increasing the temperature. The ultimate strength of
the suddenly cooled specimens was 10% lesser than that of gradually cooled columns.
Kadhum in 2013, examined experimentally the influences of temperature, load eccentricity, concrete
strength, and spacing of ties on the structural performance of 120 columns. The results showed that the
ultimate capacity of specimens decreased significantly when burning with fire flame. The effect of fire
exposure was more severe for columns tested under loads of high eccentricity. An increase in the ties
spacing caused an increment in the maximum crack width.
Bikhiet et al. In 2014, presented an experimental and theoretical study conducted on the R.C short
columns exposed to fire. In this study, fifteen specimens were constructed to investigate the effect of
Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 2 ….2016
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concrete grade, duration of fire, steel strength and the percentage of the main reinforcement. The major
conclusion was that the specimens exposed to fire failed at loads 20-40% smaller than that
corresponding unexposed specimen. The specimen constructed with high-grade steel failed at load
55% higher than that of the column with mild steel. Using the water jet in cooling down the column
reduced the residual strength by 17% compared with the column cooled gradually.
In the same year, the fire performance of light- weight concrete columns was presented by El-Shaer.
The light- weight concrete was made of expanded clay aggregate; four specimens were constructed.
The specimens were exposed to elevated temperature and subjected to an axial load. The results
illustrated that the ultimate capacity and stiffness of the unexposed light weight columns reduced
slightly compared with normal-weight columns. Perversely, the load carrying capacity of the light-
weight specimens enhanced after exposing to high temperature, the author did not show the cause of
this conclusion.
Echevarria et al. in 2015, studied the performance of protected concrete-filled fiber-reinforced
polymer tube and conventional reinforced concrete (RC) bridge columns after exposing to fire. The
specimens were similar in the axial and flexural strengths, and the study parameter was the duration of
the high temperature (one and two hours). The conventional RC columns showed lower axial strength
and stiffness retention compared to the protected columns after fire exposure.
Although of increasing the use of hollow section columns in constructions, there is a lack of
experiments conducting on the hollow columns subjected to elevated temperatures. The current paper
aims at fill this gap by introducing an experimental program. The program explored the influences of
hollow size and temperature level on the structural performance of R.C hollow columns.
2. TEST COLUMN SPECIMENS
In order to evaluate the effect of fire exposure on the structural performance of R.C. hollow section
columns loaded axially, sixteen specimens were manufactured and tested in the concrete laboratory in
the engineering College of Wasit University. The specimens were square in the cross-section with
dimensions of 120 ×120 mm; their length was 600mm. All columns were reinforced longitudinally
with four deformed bars of 10mm diameter. The bars were positioned at the ties’ corners. The
transverse reinforcement consisted of 6mm in diameter ties spaced at a distance of 120mm center to
center as sketched in Figure (1). The yield strengths of main and tie reinforcement, obtained from test,
were 436 and 381 MPa, respectively.
The test variables were the hollow size and the burning temperature. Four columns were solid and
gathered in the first group. The remaining twelve specimens were fabricated with circular hollow
sections by inserting PVC pipes longitudinally through the specimens’ center; they were classified into
three groups in accordance with the pipe diameters: 25.4, 50.8, and 76.2mm, respectively. Each group
contains four specimens, Table (1).
In all groups, three columns were burnt at 300, 500, and 700 oC temperature. The fourth specimen was
kept without the fire exposure and kept at room temperature (25oC) as a reference specimen.
The columns were designated by letter C followed by two numbers separated by hyphen symbol (-).
The first number refers to the hollow diameter divided by 25.4 while the second one refers to the
burning temperature divided by 100 (i.e. the designation C3-5 refers to a column having a hollow
Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 2 ….2016
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diameter equal to 76.2 mm and burnt at 500 oC temperature.). The second number for control
specimens was set as (0).
A one concrete mix design was utilized throughout the experimental investigation. It composed of
ordinary Portland cement, sand, and crushed gravel (10mm maximum size) in the following weight
proportions 1:1.7:2, respectively. The water to cement ratio was 0.54.
The specimens of each group were cast in one concrete batch, three standard cubes (150×150×150mm)
were taken to assess the compressive strength of batch, Table (1). Before the casting of columns, the
PVC pipes were put centrally inside the reinforcement cages as shown in Figure (2). Then, the cages
were placed inside wood moulds leaving a clear concrete cover of 10mm from all sides. The columns
were casted in the side position. A good compaction was guaranteed using a vibratory table.
3. BURNING AND TESTING
After completing the curing period (28 days), the twelve column specimens were burnt inside a diesel
furnace with 770×520×450 mm dimensions. The columns were divided into three batches (four
specimens for one batch). Each batch was burnt separately to a target temperature for one hour. The
target temperatures for three batches were 300, 500, and 700 oC, respectively. The temperature inside
the furnace was monitored through the furnace digital screen.
Next accomplishing the burning process, the furnace was turned off and its door was opened. The
specimens left inside the furnace to cool gradually as shown in Figure (3). Then, the specimens were
taken out, and their surfaces were examined accurately. Cracks distributed randomly were noticed,
they became deeper and more numerous for specimens exposed to the higher temperature as shown in
Figure (4). Moreover, these samples displayed a concrete cover spalling off, especially at their
corners. The burnt columns were kept at a room temperature before the testing.
Finally, all specimens (burnt and references) were subjected to an axial loading; the eccentricity of
load was carefully avoided. The load was applied gradually using a universal machine (150 ton
capacity) up to the specimen’s failure. Two steel plates were inserted between the specimen ends and
the testing machine to avert the problem of stress concentration. A dial gauge of 0.01 mm accuracy
was employed to measure the axial displacement of specimens as shown in Figure (5).
4. DISCUSSION OF EXPERIMENT RESULTS
The test results are discussed in three terms: mode of failure, ultimate strength of columns, and load-
axial displacement response for all samples as following.
4.1. Mode of Failure
The unexposed reference samples displayed, firstly, tiny cracks in the outer thirds of their length. The
first cracks initiated at loads of 120, 100, 75, and 50 kN for samples C0-0, C1-0, C2-0, and C3-0,
respectively; their number, depth, and width increased rapidly as the applied load increased. They
developed preliminary vertically parallel to the samples’ longitudinal axis, and thereafter they inclined
toward the column’s corners. At a collapse, the samples experienced a concrete crushing at the
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specimen’s ends, where the stress concentration was relatively high. On the other hand, the largest
hollow size sample, C3-0, spilled longitudinally at collapse load as illustrated in Figure (6).
There was a difficulty in recording the cracking loads of fire-exposed specimens. Since they displayed,
during burning, tiny cracks spreading arbitrarily on the samples’ surfaces. Generally, they suffered
concrete crushing occurring on wider area compared with unexposed similar columns. The concrete
cover spalling was observed at earlier loads, where concrete fell down as a powder, especially for
specimens burnt at 700oC. At the failure, a complete cover spalling of at corners, and concrete crushing
were noticed in the burnt columns as displayed in Figure (7). Furthermore, the largest hollow burnt
specimens did not exhibit a longitudinally split, on the contrary unexposed reference column C3-0.
4.2. Ultimate Strength of Columns
The ultimate axial loads for all samples are summarized in Table (2). The fire exposure strongly
influences the column load capacity, where the increase in the exposure temperature decreased the
column strength as plotted in Figure (8). This can be imputed to the following reasons accompanying
with elevated temperatures: the loss in a concrete strength contributing a large percentage of the
columns' strength, especially for those loaded axially. The second reason is the spalling of a concrete
cover leading to minimize the columns' cross-section area. Thirdly, a damage in the bond strength
between the reinforcement steel and the surrounding concrete besides a deterioration of the
interconnection between the concrete components as the result of a formation of earlier fire cracks. The
final cause is the expansion of the main reinforcement as well as the shrinkage of the concrete during
fire exposure.
In group one including solid specimens, reductions in the load capacity of 21.82%, 34.55%, and
52.73% were recorded for specimens C0-3, C0-5, and C0-7 exposed to 300, 500, and 700oC compared
to the unburned specimen C0-0, correspondingly.
The decreases in the columns' strength, at 300, 500, and 700oC, were :20.00%, 38.10% and 53.81% for
25.4mm hollow columns, 26.67%, 46.67%, and 62.00% in columns of a 50.8mm hollow, and 18.18%,
40.91%, and 59.09% for largest hollow columns, comparing with the corresponding unexposed
columns, respectively.
It is worth mentioning that the columns’ load capacity declined approximately linearly with raising the
temperature as illustrated in Figure (8). The best-fitting linear equations, representing the variation of
column strength with temperature, were derived using a computer program (Excel 2013), as follows.
For solid specimens,
Y=276.4-0.203X (1)
For specimens of a 25.4mm hollow diameter,
Y=212.3-0.163X (2)
For specimens of a 50.8 mm hollow diameter,
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216
Y=149.7-0.135X (3)
For specimens of a 76.2 mm hollow diameter,
Y=112.9-0.094X (4)
Where;
Y is a column ultimate strength in kN
X is a temperature fire.
Since the amount of fire- affected concrete diminished with enlarging the hollow size, the reduction
rate of column strength with temperature minimized while the hollow diameter maximized as
illustrated in Equations (1) to (4).The reduction rate was 20.3% for solid specimens, and 16.3%,
13.5%, and 9.4% for hollow specimens of diameter 25.4mm, 50.8mm, and 76.2mm, respectively.
The failure loads of all four specimens subjected to a same temperature were compared together to
evaluate the influence of a hollow size as shown in Figure (9). It can be seen that the column ultimate
load decreased rapidly as the hollow diameter increased up to (50.8 mm). Then the reduction rate
became slow, especially for specimens exposed to temperature higher than 300 oC.
The drops in the failure load for 25.4, 50.8, and 76.2 mm hollow columns compared to the
corresponding solid columns were: 23.64%, 45.45%, and 60.00% for unexposed columns, 21.86%,
48.84%, and 58.14% for 300oC fire-exposed columns, 27.78%, 55.56%, and 63.89%) columns burnt
at 500 oC, and 25.38%, 56.15%, and 65.38% for columns exposed to 700
oC, respectively.
4.3. Load-Axial Displacement Response
The curves, representing the relationships between applied load and vertical displacement, were plotted
in Figure (10) for solid specimens and in Figures (11) through (13) for specimens having a hollow
diameter of 25.4, 50.8, and 76.2mm, respectively. From these figures, it can be observed that the
columns’ axial displacement, at the same load, increased as the temperature fire raised. Because the
column’s axial stiffness dropped when they exposed to fire due to the loss in both the column’s
effective cross-sectional area and a concrete modulus of elasticity (Kodur, 2014).
In general, the load-axial deformation responses of 300 oC fire-exposed columns were very close to
those of similar unexposed columns at loads smaller than 175, 100, and 75 kN for solid, 25.4mm
hollow, and 50.8-76.2 mm hollow specimens, respectively. Since the severe fire effect, on structural
elements, takes place after exceeding 300 oC. Moreover, this rapprochement becomes clearer for
largest hollow specimens because of a reduction in the quantity of fire-affected concrete.
Finally, the presence of PVC pipes, inserted along the column samples, caused a considerable
reduction in the column’s axial stiffness due to minimizing the column’s cross-sectional area. Figures
(14) through (17) show load-vertical displacement curves for samples subjected to the same
temperature: 0, 300, 500, and 700oC, respectively. It is obvious from these figures that the axial
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displacement of columns, subject to an identical load, increased with enlarging the hollow size,
especially for columns having a hollow size greater than 25. 4mm.
5. CONCLUSIONS
The main conclusions of the current experimental program are listed as following;
1. The fire-exposed columns displayed tiny cracks after the burning processes. These cracks
distributed in a random configuration around the column’s surfaces; their number and depth
increased with elevating the temperature.
2. All column specimens experienced a compression failure, where a concrete crushing appeared at
their outer-thirds.
3. For identical columns, the axial load capacity reduced as the temperature fire raised to 300-700oC.
The corresponding reductions were: 21.82% -52.73 % for solid columns, 20.00% -53.81% for
25.4mm hollow columns, 26.67% -62.00% for specimens with 50.8mm hollow size, and 18.18% -
59.09% for 76.2 mm hollow columns, respectively.
4. The variation of columns’ strength with temperature is nearly linear. Furthermore, the reduction rate
of columns’ strength with temperature dropped as the hollow size maximized. The reduction rate
was 20.3% for solid specimens, and 16.3%, 13.5%, and 9.4% for hollow specimens of diameter
25.4mm, 50.8mm, and 76.2mm, respectively.
5. For same temperature, the column’s strength decreased with maximizing the hollow size. In the
unburnt columns, the drop in the column capacity increased to 60.00% when the hollow size
augmented to 76.2mm. The strength decline of 76.2mm hollow columns exposed to 300, 500, and
700 oC were 58.14%, 63.89%, and 65.38%, compared to the corresponding solid columns,
respectively.
6. The columns’ axial stiffness descended as the temperature fire and the hollow size increased,
especially for columns having a hollow size greater than 25.4 mm and burnt at temperature
exceeding 300 oC.
6. REFERENCES
[1] Bikhiet, M.M., El-Shafey, N.F., and El-Hashimy, H.M, 2014, "Behavior of Reinforced
Concrete Short Columns Exposed to Fire", Alexandria Engineering Journal, Vol.53, No.3, PP.643-
653.
[2] Echevarria A., Zaghi A.E, Christenson, R., and Plank, R., 2015, "Residual Axial Capacity
Comparison of CFFT and RC Bridge Columns after Fire" Polymers Journal, Vol.7, No. 5, May, PP.
876-895.
[3] El-Shaer, M.A., 2014, "Structural Analysis for Concrete Columns Subjected to Temperature",
ACTA TEHNICA CORVINIESIS –Bulletin of Engineering, Vol. IV, No.2, April-June, PP. 69-81.
Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 2 ….2016
218
[4] Izzat, F.A., 2012, "Effect of Fire Flame (High Temperature) on the Behavior of Axially Loaded
Reinforced SCC Short Columns" Journal of Engineering, Vol.18, No.8, August, PP.889-904.
[5] Kdhum, M.M., 2013, "Effect of Burning on Load Carrying Capacity of Reinforced Concrete
Columns", Journal of Babylon University/Engineering Sciences, Vol.21, No.4, PP.1194-1212.
[6] Kim, T.H., Seong, D.J., and Shin, H.M., 2012, "Seismic Performance Assessment of Hollow
Reinforced Concrete and Prestressed Concrete Bridge Columns" International Journal of Concrete
Structures and Materials, Vol.6, No. 3, May, PP. 165-176.
[7] Kodur, V.R.K., "Properties of Concrete at Elevated Temperatures", ISRN Civil Engineering,
Vol.2014, 2014, PP.1-15.
[8] Kodur, V.R.K., Bisby, L.A., Green, M.F., and Chowdhury, E., 2005, "Fire Endurance
Experiments on FRP-Strengthened Reinforced Concrete Columns", National Research Council of
Canada, Institute for Research in Construction, Research Report No.185, March, 41pp.
[9] Sakai, K., and Sheikh, S.A., 1989, "What Do We Know About Confinement in Reinforced
Concrete Columns", ACI Structural Journal, Vol.86, No.2, Mach-April, PP.192-207.
Table (1): Details of Test Specimens.
Group
No.
Column
Designation
Hollow
Diameter(mm)
Temperature oC
Concrete
Compressive
Strength (MPa)
1
C0-0
0.0
25
31.5 C0-3 300
C0-5 500
C0-7 700
2
C1-0
25.4
25
32.2 C1-3 300
C1-5 500
C1-7 700
3
C2-0
50.8
25
33.6 C2-3 300
C2-5 500
C2-7 700
4
C3-0
76.2
25
31.1 C3-3 300
C3-5 500
C3-7 700
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219
Table (2): Specimens’ Collapse Loads.
Group
No.
Column
Designation
Temperature oC
Collapse
Load (kN)
% Decrease
in Collapse
Load
1
C0-0 25 275 reference
C0-3 300 215 21.82
C0-5 500 180 34.55
C0-7 700 130 52.73
2
C1-0 25 210 reference
C1-3 300 168 20.00
C1-5 500 130 38.10
C1-7 700 97 53.81
3
C2-0 25 150 reference
C2-3 300 110 26.67
C2-5 500 80 46.67
C2-7 700 57 62.00
4
C3-0 25 110 reference
C3-3 300 90 18.18
C3-5 500 65 40.91
C3-7 700 45 59.09
Figure (1): Details of Column
Specimens.
(a) Specimens
dimensions
(b) Solid columns (c) Hollow columns
(diameter=25.4mm)
(d) Hollow columns
(diameter=50.8mm)
(e) Hollow columns
(diameter=76.2mm)
All dimensions in
mm.
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220
(a) Positioning the PVC pipe at the
reinforcement cage center
(b) Preparing the reinforcement cage
Figure (2): Details of Reinforcement for
Column Samples.
Figure (4): Typical of Fire Cracks
Distributed Randomly over The Specimen
Surface.
Figure (3): Gradually Cooling of
Specimens.
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221
Column specimen
Figure (5): Sample Being Tested.
Dial gauge
Fixed part
Moveable part,
moves upward to
apply the load
(a) Column C1-0 (b) Column C2-0
Figure (6): Crack Patterns for Unexposed Specimens.
(c) Column C3-0
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222
0
50
100
150
200
250
300
0 200 400 600 800 1000
Lo
ad
(k
N)
Temperature (ᵒC)
solid
25.4 hollow
50.8 hollow
76.2 hollow
0
50
100
150
200
250
300
0 20 40 60 80 100
Lo
ad
(k
N)
Hollow Size (mm)
0ᵒC
300 ᵒC
500 ᵒC
700 ᵒC
Figure (8): Column’s Strength versus
Temperature. Figure (9): Column’s Strength versus
Hollow Size.
(a) Column C1-7 (b) Column C2-7
Figure (7): Crack Patterns for Specimens Exposed To 700 OC.
(c) Column C3-7
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223
Figure (10): Load-Axial Displacement for
Solid Specimens
0
50
100
150
200
250
300
0 2 4 6 8 10
Lo
ad
(k
N)
Axial Displacement (mm)
C0-0
C0-3
C0-5
C0-7
0
50
100
150
200
250
0 2 4 6 8 10
Lo
ad
(k
N)
Axial Displacement (mm)
C1-0
C1-3
C1-5
C1-7
Figure (11): Load-Axial Displacement for
25.4 mm Hollow Specimens
0
25
50
75
100
125
150
175
0 2 4 6 8 10
Lo
ad
(k
N)
Axial Displacement (mm)
C2-0
C2-3
C2-5
C2-7
0
25
50
75
100
125
0 2 4 6 8 10
Lo
ad
(k
N)
Axial Displacement (mm)
C3-0
C3-3
C3-5
C3-7
Figure (12): Load-Axial Displacement for
50.8 mm Hollow Specimens
Figure (13): Load-Axial Displacement for
76.2 mm Hollow Specimens
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0
25
50
75
100
125
150
175
200
0 2 4 6 8 10
Lo
ad
(k
N)
Axial Displacement (mm)
C0-5
C1-5
C2-5
C3-5
Figure (16): Load-Axial Displacement
Specimens Exposed to 500oC
0
25
50
75
100
125
150
0 2 4 6 8 10
Lo
ad
(k
N)
Axial Displacement (mm)
C0-7
C1-7
C2-7
C3-7
Figure (17): Load-Axial Displacement
Specimens Exposed to 700oC
0
50
100
150
200
250
0 2 4 6 8 10
Lo
ad
(k
N)
Axial Displacement (mm)
C0-3
C1-3
C2-3
C3-3
0
50
100
150
200
250
300
0 2 4 6 8 10
Lo
ad
(k
N)
Axial Displacement (mm)
C0-0
C1-0
C2-0
C3-0
Figure (14): Load-Axial Displacement
Unexposed Specimens
Figure (15): Load-Axial Displacement
Specimens Exposed to 300oC